If your horn is a good instrument in otherwise resonably good shape, here is the best way to fix it: Carefully put the horn in the bag or case, load it up in your car and take it to the nearest, competent repairman. Once he or she has finished the work, write out a check for the amount of the repair and thank him (or her) sincerely for fixing the damage.

You have admitted that you have minimal tools and no experience. That is a recipe for disaster. By the way, ask if you can watch while the repairman fixes the horn. You will be suprised at the amount of skill required for the job.